I've been following this thread with interest and thought I'd put a club organiser's point of view.

Our folk club is primarily a singers club and we have a lot of performers amongst our regulars. Until quite recently, quite a few of these didn't come on guest nights, but we seem to have brought them round. We expect 25 - 40 in the audience for a guest night (can't fit any more in) and expect to make up the artists fee from other revenue. We keep our prices down, but pay the artist what they as for rather than a percentage. We can't book big names or bands (but we do run special nights in a different venue with these.) Our club guest nights are always with artists requested by our members and we hardly ever have the same artist twice. I would hate to see the same roster coming round year after year. I think we would lose our audience if we did that.
This way of working is hard on unknown performers - I think I've only taken a risk twice - but overall I think it is fair.
BTW as an occasionally paid performer, I admit to being one of those who only wants gigs in school holidays (but not for much longer as I retire in three weeks time!)